For example, there is an internal combustion engine mounted to a vehicle including an auxiliary intake path opened to a downstream side of a throttle valve of an intake path and communicating with the atmosphere, a control valve for controlling an auxiliary air amount (idling intake amount) supplied to the internal combustion engine via the auxiliary intake path, and a fuel supplying unit for supplying a predetermined fuel amount in accordance with a total intake amount including the auxiliary air amount to a combustion chamber of the internal combustion engine, in which a predetermined rotational position of the internal combustion engine is detected and the control valve is opened in synchronism with a signal of the predetermined position (refer to, for example, Patent Reference 1).
(Patent Reference 1) JP-B-63-60219 (pages 1-7, FIGS. 1-4)
According to a controller of an internal combustion engine for controlling a fuel supply amount of the fuel supplying unit by detecting an intake pressure of the intake path by an intake pressure detecting unit arranged on the downstream side of the throttle valve of the intake path, when the auxiliary intake path is connected to the downstream side of the throttle valve of the intake path and the control valve of an opening/closing type is used, there is a case in which by a change in the intake pressure by operating to open and close the control valve, despite a steady state, the state is erroneously determined to shift to an accelerating or decelerating state and an idling rotational speed becomes unstable.
In addition, when a threshold of the change in the intake pressure for determining that the state is shifted to the accelerating or decelerating state in order to avoid the case, drivability in opening the throttle valve intended by a driver is deteriorated.
Further, according to a system which is not provided with a stroke determining sensor for determining a stroke of the internal combustion engine by detecting the intake pressure of the intake path, when a condition of a number of times of establishing stroke determination is increased in order to avoid that the stroke of the internal combustion engine cannot be determined based on a similar cause, starting performance of the internal combustion engine is deteriorated.
When a ratio of a time period of opening the control valve within a predetermined time period is controlled (duty control), in consideration of a fluctuation in rotation of the internal combustion engine, the control to open and close the control valve becomes complicated and a calculating load is increased.
When a user changes to set the idling rotational speed to be low, a fluctuation in rotation of the engine is increased and there is a case that the idling rotational speed cannot be controlled stably.
The invention has been carried out in view of such a situation and it is an object thereof to provide an idle rotational speed controller, a controller of an internal combustion engine and an internal combustion engine, which enable stable idling operation.